Process for producing microcellular shaped pieces of dimensional accuracy, particularly shoe soles

ABSTRACT

The invention relates to a process for the manufacture of microcellular shaped pieces, particularly shoe soles, in several vulcanization stages. In the first step, there is compounded a stock containing an elastomer, a plastomer and/or a thermoplastic elastomer, a blowing agent, an accelerator system and usual compounding ingredients used commonly in the rubber industry, e.g. plasticizers and fillers. This stock is prevulcanized and partially cross-linked in a closed mould under pressure at a temperature and for a time determined by the accelerator system, and the prevulcanized stock is expanded. In a further vulcanization phase, this prevulcanized, expanded semiproduct is completely vulcanized in a closed mould, and finally, the completly vulcanized product is cooled under pressure in a closed mould thereby hardening the component and stabilizing the final product in its predetermined form. By the aid of the invention, it has become possible to eliminate the phenomenon of postexpansion and postshrinkage, respectively, in the case of vulcanized, microcellular product, as a result of which in the second vulcanization stage there are produced shaped pieces of high dimensional accuracy and of a low apparent density (0.2 to 0.7 g/cc) having uniformly distributed cells, and the strength properties of which comply with every practical requirement.

United States Patent Dinzburg et al.

PROCESS FOR PRODUCING MICROCELLULAR SHAPED PIECES OF DIMENSIONALACCURACY, PARTICULARLY SHOE SOLES Inventors: Boris Nisonovich Dinzburg;Jury Alexandrovich Smetkin; Vladimir Iosifovich Alexenko; VsevolodAndreevich Mikhailov, all of Moscow, USSR; Dr. Ivan Lrirant, Budapest,Hungary; Gyt'izii Seltenreich, Dunakeszi, Hungary; Jend Keszei,Budapest, Hungary; Gyfirgy Marlon, Budapest, Hungary; Albert Balazsfai,Budapest, Hungary; Jenr'i Donath, Budapest, Hungary; Ernt'i Biilcskei,Budapest, Hungary Assignees: Bor-, Mubor-Es Cipoipari Kutato Intezet,Parsi Jozsef, Budapest, Hungary; Vsesojuzny Nauchno-IssledovatelskyInstitut Plenochnykh Materialov i Iskusstevennoi Kozhi, Moscow, U.S.S.R.

Filed: Feb. 13, 1973 Appl. No.: 332,090

Related US. Application Data Continuation of Ser. No. 96,738, Dec. 10,1970, abandoned.

Foreign Application Priority Data Dec. 30, 1969 Hungary 1210 US. Cl.264/54; 264/51; 264/55; 264/244; 264/347 Int. Cl B29d 9/00; B29h 7/20Field of Search 264/51, 54, 55, 236, 244, 264/347 [56] References CitedUNITED STATES PATENTS 2,296,305 9/1942 Roberts 264/55 2,297,022 9/1942Pfleumer..... 264/55 2,570,182 10/1951 Daly et a1. 264/55 2,650,3909/1953 Capdevila.,. 264/244 3,003,192 10/1961 Pfleumer..... 264/553,751,534 8/1973 Oxley 264/54 Primary ExaminerRonald W. GriffinAttorney, Agent, or FirmYoung & Thompson [57] ABSTRACT The inventionrelates to a process for the manufacture of microcellular shaped pieces,particularly shoe soles, in several vulcanization stages. In the firststep, there is compounded a stock containing an elastomer. a plastomerand/or a thermoplastic elastomer, a blowing agent, an accelerator systemand usual compounding ingredients used commonly in the rubber industry,e.g. plasticizers and fillers. This stock is prevulcanized and partiallycross-linked in a closed mould under pressure at a temperature and for atime determined by the accelerator system, and the prevulcanized stockis expanded. ln a further vulcanization phase, this prevulcanized,expanded semiproduct'is completely vulcanized in a closed mould, andfinally, the completly vulcanized product is cooled under pressure in aclosed mould thereby hardening the component and stabilizing the finalproduct in its predetermined form.

By the aid of the invention, it has become possible to eliminate thephenomenon of postexpansion and postshrinkage, respectively, in the caseof vulcanized, microcellular product, as a result of which in the secondvulcanization stage there are produced shaped pieces of high dimensionalaccuracy and of a low apparent density (0.2 to 0.7 g/cc) havinguniformly distributed cells, and the strength properties of which complywith every practical requirement.

3 Claims, 14 Drawing Figures FiJENTEB Z B SHEET 2 OF 5 Fig.3d

PEA! MEIHEL P129193 SHEET W 5 3.880.970

FigAcl PROCESS FOR PRODUCING MICROCELLULAR SHAPED PIECES OF DIMENSIONALACCURACY, PARTICULARLY SHOE SOLES This is a continuation of applicationSer. No. 96,738. filed Dec. 10, 1970, now abandoned.

A great variety of porous rubbers and plastics varying from articleswith totally open intercommunicating cells to articles with fully closedcells are well known in the art. In many fields, for example. in theshoe manufacturing solely expanded rubbers with fully closed cells areof importance as only these materials meet the requirements of shoemanufacture.

The making of expanded rubbers with closed cells, commonly calledmicrocellular rubbers by which title they will be referred tohereinafter, involves expanding. One prior art process has been tocalender the relatively soft rubber mixture into a sheet or rod stock,to place this stock in an autoclave and to fill it up with ahigh-pressure gas (at least 200 atm.) for example, with nitrogen,whereupon a portion of said gas dissolves under the high pressure in therubber stock, further after vulcanisation to reduce the pressure byopening the mould whereupon the gas dissolved in the rubber stockexpands and produces closed cells within the stock.

A more advanced process has been to add blowing agents to the cruderubber stock intended to be vulcanized in mould and heat this mixture,whereupon the blowing agents decompose to gaseous products whichdissolve partly or entirely under the high pressure.

By heating the mixture this is cross-linked (vulcanized). and by openingthe mould the pressure is reduced, whereupon the gaseous products expandand produce closed cells within the stock. For blocking mould partinglines the mould has been overcharged by more than 3 7(.

A feature in most of the above-mentioned various processes is the use ofmoulds with conical splits.

In the one-stage vulcanizing process the stock begins to expand whenvulcanization is terminated. A disadvantage of the process is that inpractice it is difficult, if not impossible, to produce a final product,the dimensions of which after expanding correspond to the requireddimensions. In the course of production the rubber stock grows in bulkto the multiple of its previous volume, later same goes through ashrinkage of about 3-25 70 which may keep on during storage. No shapedpieces of dimensional accuracy having an apparent density less than 0.7g/cm may be produced by any one of these processes only less accurateones having an apparent density of 0.7-0.9 g/cm.

In most cases two or multistage vulcanization processes are employed forproducing microcellular shaped pieces which processes comprise aprevulcanization stage (temporary cross-linking) and one or moresubsequent vulcanization stages (curing). It is in the nature of themultistage techniques that the microcellular structure produced byexpansion in the relatively plastic stock during the prevulcanizationstage has to be stabilised by a final vulcanization.

One of the known two-stage processes of the art has been to achieve thefirst vulcanization stage in mould and to perform the second, orsubsequent stages in or outside the mould. In this way there may beobtained microcellular sheets or shaped pieces of apparent density of0.3-0.7 g/cm Although the extent of shrinkage of these products is lessthan that of shaped pieces made by the one-stage process, as the extentof the strains arising during expansion is also less, it is adisadvantage of this method that it is difficult, if not impossible, toensure a dimensional accuracy to the shaped pieces as the extent of thecontraction cannot be controlled.

A known two-stage method has been to add blowing agents which decomposeat a higher temperature than the vulcanization temperature to the rubberstock, and in the first stage to vulcanize the stock 15 minutes at atemperature of C whereupon the stock grows in bulk to the manifold ofits original volume, then to cure the intermediate product obtained in aclosed mould in the usual way.

Since the first vulcanization stage is carried out free, withoutapplying pressure a disadvantage of this method is that the cells of thefinal product are largesized, that is to say, the product has nomicrocellular structure hence it follows that its strength propertiesare worse than the properties of products having a microcellularstructure. By means of this method no shaped piece of good quality andof dimensional accuracy having embossed pattern and the dimensions ofthe parts of which varies from place to place within same piece may beproduced.

Another prior art process has been to employ press mould includingplungers built into the mould, to fill up completely the mould with thestock and to vulcanize the stock under a determined specific pressure inthe usual way and not to open the mould after the prevulcanization iscomplete but to release the plunger which is pressed upwards by thepressure of the gas to a determined extent which is the intended heightof the shaped piece, hence it follows that the stock expands only in onedirection. The complete vulcanization is achieved at a temperature equalto the prevulcanization temperature.

It is a disadvantage of this process that the stock expands only in onedirection and owing to this fact there may be obtained only such shapedpieces of inhomogeneous structure, in which the thick walled cells ofvarious sizes are unevenly dispersed. Neither this process allows ofproducing embossed shaped pieces of low apparent density and ofdimensional accuracy and the thickness of parts of which varies withinsame shape.

It is an object of the present invention to provide an efficient.process for producing microcellular shaped pieces of dimensionalaccuracy and of low apparent density (less than 0.7 g/cm) in any formand embossed with any pattern at will and the thickness of which varieswithin same piece and the cells of which are of the same size, andhaving high strength properties and complying with standardspecifications and not shrinking during storage and which are suited tobe fastened by vulcanization to other shaped parts, e.g. to shoe upperparts.

The invention includes a process for the manufacture of microcellularshaped pieces described above which comprises compounding a stockcontaining an elastomer, a plastomer the melting temperature of which isequal to or less than the temperature of the first vulcanization stage,and/or a thermoplastic elastomer, a blowing agent, the decompositiontemperature of which in the particular stock is equal to or less thanthe temperature of the first vulcanization stage, an accelerator systemwhich induces fast cross-linking in the first vulcanization stage andtogether with the vulcanization temperature and vulcanization timeprovides a minimum rate of vulcanization in the -70 7: cross-linkingrange, and usual compounding ingredients used in the rubber industry,e.g. plasticizers and fillers; further vulcanizing and partiallycross-linking said stock in a closed mould under pressure at atemperature and for a time determined by the accelerator system, in thefirst vulcanization stage, expanding the prevulcanized stock thencompletely vulcanizing the prevulcanized, expanded semi-product, cut tomeasure in particular cases, in a closed mould the form and dimensionsof which are equal to the form and dimensions of the final product underpressure and at temperature determined by the composition of the stockin question in the second and/or subsequent vulcanization stages;further cooling the completely vulcanized product under pressure in aclosed mould thereby hardening the plastomer component and stabilizingthe final product in a form which corresponds to the form of the closedmould in the final vulcanization stage.

In certain cases it is expedient to modify the volume of the press toolbetween the first and second vulcanization stage.

A characteristic feature of the invention is that the pressure requiredto prevulcanization of the crude stock is provided in the closed mouldthe form and dimensions of which are equal to the form and dimensions ofthe final product by the pressure of a liquid conducted into said mouldwhere said liquid surrounds the stock to be vulcanized, further that theexpanding of the prevulcanized stock is achieved through reducing thepressure by way of discharging said liquid whereby the prevulcanizedstock fills completely in the closed mould, further that theprevulcanized stock is vulcanized completely in the second vulcanizationstage.

According to the present invention for pressing medium hot liquid isused in the prevulcanization stage whereby both the pressure and thetemperature required to the vulcanization are simultaneously provided.

Another characteristic feature of the invention is that the shapedpiece, for example shoe sole, cross-linked to some extent in the firstvulcanization stage, is simultaneously attached by way ofa second and/orsubsequent vulcanization stages to another shaped piece or pieces madeof some structural material, for example: metal, plastics, rubber,leather, for example to shoe upper part. This attaching may be carriedout by spreading thermoplastic cement over the recepting pieces andjoining up the cemented piece to the prevulcanized shaped piece andstabilizing this bond by a second vulcanization stage. Choice of asuitable adhesive is, of course, dependent on the particular material inquestion.

The process of this invention has many advantages which other knownprocesses of the art do not dispose of.

By the aid of the process of present invention it has become possiblefor the first time to eliminate the phenomenon of postexpansionrespectively postshrinkage in the production of vulcanized microcellularproducts, as a result of which in the second vulcanization stage thereare provided shaped pieces of high dimensional accuracy and of adesirable low apparent density (0.2-0.7 g/cm) having uniformlydistributed cells and the strength properties of which comply with everyrequirement of the practice. Those shaped pieces may be attached byvulcanization to other structural pieces, for example shoe soles to shoeupper parts, but as a matter of course these microcellular shaped piecesof various configuration may be attached also to structural pieces madeof metal, plastics, etc. There is no loss of material when processing,as the cutting waste left over in the clicking procedure which followsthe first vulcanization stage may be reprocessed. The moulds suitablefor use in the practice of this invention are constructionally simple,not too expensive, and are easily handled.

The invention will be more clearly understood by reference to followingExamples which are pure illustrative. Table 1. illustrates some suitablecrude stock mixtures.

Table No. l

Formulation of compounds (Parts by weight) I 2 3 4 Constituents Thechoice of materials for compounding is not, of course, confined tomaterials enumerated in Table 1., all those materials may be eligiblewhich comply with the stipulations referred to above, that is to say:accelerator systems which induce fast crosslinking as a function of timeand temperature in the first vulcanization stage and provides a minimumrate of vulcanization in the 20-70 cross-linking range; blowing agentsthe decomposition temperature of which in the particular stock is equalto or less than the temperature of the first vulcanization stage;plastomers the melting temperature of which is equal to or less than thetemperature of the first vulcanization stage. In this way for elastomerinstead of synthetic styrene-butadiene rubber following may be employed:acrylnitrile rubber, polyehloroprene, polybutadiene, polyisoprene, etc.For plastomer, for example, polystyrene or PVC may be used instead ofpolyethylene. The plastomer-elastomer mixture may be substituted by ormixed with all other thermoplastic elastomers. For rubber resin insteadof Butakon S 8551 of high styrene content indicated in Table 1 otherrubber resins may be considered. For blowing agent in place of theindicated dinitroso-pentamethylenetetramine also azodicarbonamide orbenzenesulphydrazine, etc. may be employed. For accelerator system as arule guanidine derivatives and amine accelerators, benzthiazolederivatives or all these jointly may be used.

The components of the stock partly exert an influence over theproperties of the final product partly determine to a certain extent theparameters of the vulcamould must provide a uniform heating up of thesame extent in every part of the crude shaped piece. It is inexpedientto exceed the temperature of 145C. in the first vulcanization stageconsidering the postulate relating to vulcanizing at a minimum oftemperature. The length of time of the prevulcanization stage is 5-35minutes. preferably -20 minutes (see Table 2.) depending on the appliedvulcanization temperature. In this stage the stock becomes onlypartially cross-linked 10 while the blowing agent completely decomposesto gas- Table No. 2

Parameters of Vulcanization Stock Stock Conand indices of strength Unit(no cuttings) taining Cuttings properties 1 2 3 4 5 6 Time ofcross-linking of the first vulcanization stage minute 10 10 10 10 IOTemperature of cross-linking of the first vulcanization stage C 130 130130 Time of cross-linking of the second vulcanization stage (aftervulcanization) minute l0 l0 10 Temperature of cross-linking of thesecond vulcanization stage (after vulcanization) "C 160 160 160 Tensilestrength before aging kp/cm 38 46 40 Tensile strength after aging kp/cm46 39 36 Elongation at break before aging 225 312 255 Elongation atbreak after aging 7! 245 208 223 Permanent elongation (at elongation of30 71 4.5 3.0 4.0

Permanent deformation (under pressure/2 h,

Tear propagation kp/cm 6,7 6.2 6.5

Softness 76 78 Shrinkage at 25C after days 71. 0.5 0.5 0.5

Shrinkage at 70C in:

8 hours 7: 2.7 2.3 2.3

Apparent density g/cm 0.4 0.39 0.4

Bending strength kilomore than cycles 25 25 25 After mixing of the stockis completefor example achieved according to formulae indicated aboveand by usual rubber techniques, it is expedient to perform thepreceeding mixing-up of the elastomer and the plastomer at the meltingtemperature of the thermoplast 50 the stock is calandered on a profilecalander or extruded through a profile orifice to sheets. This procedureis followed by the first stage of vulcanization. After vulcanization itis required that the degree of cross-linking of the intermediate productbe minimal 55 and of the same value in all parts of various thickness.Only observance of this condition provides a suitable reshapeability, auniform microcellular structure and the reprocessability of thecuttings. Therefore the first vulcanization stage has to be achieved atthe lowest 60 eous products. The prevulcanized intermediate products areexpanded free or in the mould itself.

After this procedure the prevulcanized expanded intermediate productgets into the second stage of vulcanization where it is put into a mouldthe form and dimensions of which are equal to the form and dimensions ofthe final product, and where the cross-linking of the stock is completedin the case of mixtures according to Table 1. This procedure is carriedout in 5-10 minutes under a pressure of 5-55 kg/cm preferably of 20kg/cm at a temperature that is higher than the prevulcanizationtemperature, at about -200C, preferably at C. The parameters ofpressure. temperature and time as corresponding parameters of the firstvulcanization stage may of course come up to different values in case ofother mixtures.

At the end of the second vulcanization stage prior to reducing pressure,that is to say, prior to opening the press tool, the vulcanizedmicrocellular product is expediently cooled down to room temperature.the press will be opened only after cooling is complete, then the shapedpiece is removed from it. The plastomer being in the stock becomes hardon the effect of cooling and stabilizes the shaped pieces. The finalproduct, the form anddimensions of which are equal in every direction tothe form and dimensions of the vulcanizing interior of the press mould,undergoes no expansion, consequently no shrinkage any more. As a resultof the process shaped microcellular pieces of dimensional accuracy andof low apparent density may be obtained. Namely the developed gasproducts expand the prevulcanized stock and the second vulcanizationstage, to which the high temperature and pressure required to developfinal shape is at the same time provided by way of the simultaneouslyexpanding gas, stabilizes the expanded structure. In the cooling stagethe gas pressure in the cells decreases and the thermoplastic components(plastomers) strengthen and stabilize the cell walls. As a result of itno subsequent dimensional change in the shaped microcellular piece willany longer take place and the piece retains its shape, for example, likeplaster casting.

Further advantage of the process of present invention are that owing tothe technique described above any embossed pattern may be accomplishedon the surface of the shaped piece simultaneously with the vulcanizingprocedure and that the cuttings derived from clicking may be reusedomitting the usual reclaiming process without any falling-off inquality. Clicking is carried out namely after the first vulcanizationstage when the cross-linking has not yet been completed. The cuttingsmay be reused without further ado for basic component of the stock.

The vulcanization of the basic stock containing basically samecomponents may be achieved very advantageously by the process describedabove according to which the basic stock the dimensions of which aresmaller than the dimensions of the press tool cavity, is subjected to ahydraulic pressure and the induction of heat quantity required to thevulcanization is achieved expediently by the pressing medium itself. Forthis purpose the use of highly pressurized hot water seems to be themost obvious solution. This process is achieved. among others. on thesame parameters indicated above and in the same way and the indices ofthe product obtained in this way are of the same value.

The press tool suitable for use in the process according to theinvention is illustrated in the accompanying drawings from which alsofurther advantages of the process of the invention will appear, whereFIG. 1 represents a longitudinal section of a prevulcanizing press toolwith restricted thermal conduction.

FIG. 2 represents the longitudinal section of another prevulcanizingpress tool having divided temperature ranges.

FIG. 3a3d show an after-vulcanizing pressing tool suitable both forachieving heating and cooling; FIG. 3a and 3b represent the section ofthe press tool, FIG. 3c and 3d represent the view of the inner side ofthe upper plate respectively of the lower plate.

FIG. 4a-4e represents an universal hydraulic operated press toolsuitable for achieving both the two vulcanization stage and the cooling.

FIG. 6 represents similarly the view in perspective of an universalpress tool suitable for achieving both :stages.

The two-piece press tool according to FIG. 1. is composed of the lowermould part 1 and of the upper mould part 2 abutting to former. Outerside sections of both upper mould part 1 and of lower mould part 2 wherethe thickness of the crude stock 3 is less, are covered by heatinsulating insets. The heating plates of the known press non representedin the figure are denoted by reference numbers of 5a and 5b.

By the layout of the press tool of determined or limited heat conductionthe vitally essential condition of the process of the invention may beensured, vis. that every point of the stock becomes cross-linked duringprevulcanization, say, in the course of the first vulcanization stage,independently of the differences in the thickness of the stock and thatthe degree of the vulcanization actually achieved be the same in everypart of the stock. Due to the insulating insets the heat uptake of thestock is commesurate with its thickness, the various parts of theprofiled sheet get various quantities of heat. Where less heat isrequired to there heat insulating insets are placed.

The prevulcanization using the press tool of the present invention isachieved in the following way: the crude profile stock 3 is put into thecavity of the lower mould part 1 then the upper mould part 2 is placedon the top of it and both mould parts are placed in between the heatingplates 5a and 5b of the press and are pressed together, the suitablymeasured heat insulating insets 4 ensure that various quantitiescommensurate with the thickness come to the thicker or thinner parts ofthe stock 3. By this way the required degree of uniform prevulcanizationactually achieved and a homogeneous cross-linking of the wholeintermediate product which is sensitive to temperature variations, areguaranteed. The intermediate product thus obtained is remarkablysuitable for starting material in the further processes of the presentinvention and its cuttings may be reused omitting the usual reclaimingprocesses.

FIG. 2. represents another prevulcanizing press tool having devidedtemperature ranges. Its aim is also to provide a uniform cross-linkingin the intermediate product. With a view to it there must be transmittedless heat to the thinner section in zones A while more heat to thethicker sections in zones B.

This procedure is achieved by steam pipe systems arranged in the presstool consisting of the die 6 and cover 7 and operated by various steampressures. In zones A a steam pipe system consisting of 8 pipes and inzone B a steam pipe system consisting of 9 pipes are built into the die6 and cover 7. The steam channel systems are joined by a pressureregulator not represented in the figure to the steam generator, by whichit may be attained that various quantities of heat come to the diverselythick parts of the crude profile sheet in a determined unit of time.

The use of the press mould is to put the crude profile sheet 3 into thecavity 6a of the die 6 then to close the die by the cover 7. The pressmould is set in the press and a pressure of required extent is appliedon it. Steam of various pressure is admitted into the steam channelsystems of zones A and B; into zones B which correspond to the thickersections of the product there is admitted a high-pressure steam and alow-pressure steam into zones A which correspond to the thinner sectionsof the product. Thus admitting various quantities of heat to the thickerand thinner sections of the crude profile sheet 3 a cross-linking of thesame extent is attained in the profile sheet. After prevulcanization theprevulcanized profile sheet is expanded and after having been cooleddown is clicked into a suitable form and subjected to a secondvulcanization stage. Since in the course of prevulcanization thecross-linking is homogeneous and only partial the cuttings deriving fromclicking may be reused.

FIGS. 3a3d represent a pressing tool suitable for carrying out thesecond vulcanization and then the cooling stage in confirmity with theprocess of present invention. The press tool has a direct heating andcooling system. The press mould consists of three main parts: the lowerplate 10, the upper plate 11 and the proper press tool 12, which may beplaced in between them. The wall thickness of the press tool is minimalfor the sake of lightness and fast heat transfer. Its form anddimensions correspond to the form and dimensions of the product to beshaped. A bossing conforming to the embossed design to be formed on thefinal product may be engraved into the inner surface of the press tool12. For paralleling the profile sheet and the press plate a separateadjusting plate may be used. Both the lower and the upper plate arefitted out with a channel system suitable for conducting the heating,respectively the cooling medium and consisting of channels 13. For anadequate insulation packings 15 are placed between the lock plate 14 tobe put on the upper plate 11 just as well as between the lower'plate land the press tool 12. In addition the top and bottom surfaces of thepress mould are covered with heat insulating plates l6, l7, 18, 19 inorder to avoid warming up of the press into which the press mould,represented in FIG. 3a-3d, has been placed. The vulcanization mould 12is replaceable. its inner form and dimensions may be shaped in variousways and thus the press tool is suitable for manufacturing a greatvariety of products. The parts of the press tool are pressed together byclamping screws 20. On the lower part of the upper plate 11 there isarranged a heel block 21. The set consisting of single tool parts issteered by slightly conical pins 22.

The working process by use of the press tool described above is thefollowing:

The clicked crude stock not represented in the figure is placed into thevulcanizing mould l2 and is covered by the upper plate 11. Then thepress mould is put into the press and pressed together by a properpressure.

Hot steam of a given pressure is admitted into the channels of the presstool 13, hereby providing the temperature required to the second stageof the vulcanization. On the action of heat and pressure the viscosityof the polymer mixture decreases, expands and filling in the inner spaceof the press mould takes on its shape while exerting pressure on theinner walls of the press mould. The product takes shape and theprocedure of the development of the structure is enacted.

After the termination of the vulcanization cold water is admitted intothe channels 13 in order to cool down the product. Then the press mouldis opened and the final product is removed.

An advantage of the press tool described is that it is possible toaccomplish both the vulcanization and the cooling of the product in theclosed vulcanizing mould itself since the press must not be heatedrespectively cooled but only the vulcanizing mould. In this way timerequired so far to heat up the press together with the mould may beeliminated and the loss in heat may be reduced to a minimum for whatthere was no possibility in the case of presses known so far where theheating was achieved through the plates of the press. The reduction ofthe mass to be heated up on the press also promotes the heat lossdecrease.

In order to increase the efficiency of the heating respectively coolingit is expedient to arrange several press tools in one press block and toachieve the admission of the heating, respectively cooling medium byparallel connection.

FIGS. 4a4d represent similarly a press tool suitable for achieving thesecond vulcanization and the cooling stage which may be heated andcooled down independently of the press and which automatically clicksprofile sheets out of the rubber stock.

Main parts of the press tool are as follows: upper plate 23, lower plate24, press mould upper part 25a, press mould lower part 25b, and a pressknife 26 tallying with the contour line of the sole and encercling it,thus suitable for achieving the clicking operation and whichsimultaneously close the sides of the mould. The press mould parts 25aand 25b and the press knife 26 jointly constitute the mould cavity 27into which the intermediate product is placed.

The upper mould part 25a is fastened by adjustable screws to the upperplate 23 while the lower mould part 25b is fixed to the lower plate 24.The upper and lower mould parts are aligned with the mould cavity 27 bythe aid of carrier pins 30. The space 31 serves for taking up thecuttings of the cut out intermediate product. The thickness of theprofile sheet to be vulcanized may be determined by alteration of theintermediate space between the lower mould part 250 and the upper mouldpart 25b. The alteration is carried out by the aid of adjusting screws.

In the sleeve 35 enclosed bush 32 serves for receiving the carrier pin30. There is a groove 33 in the central part of the carrier pin 30 whilein the wall of the bush there is a ball socket 33 for receiving the ball34 and which registers into the groove 33. These structural membersjointly constitute the automatic locking device of the press tool.

The mode of operation of the self-clicking press tool in conformity withpresent invention is as follows:

In the starting cycle (FIG. 4b) the upper plate 23 together with the 25bupper mould part as well as the cutting knife 26 are in upper position.The profile sheet made of ',crude rubber mixtures 28 is placed into themould cavity 27.

In the second cycle (FIG. 40) the upper plate 23 together with the uppermould part 25b is slided downwards thereby pressing together the profilesheet 28.

In the third cycle (FIG. 4d) the cutting knife 26 is moved downwards andby the aid of its cutting edge a piece the form of which accuratelyconforms to the final form of the end-product is clicked out of theprofile sheet.

In the fourth cycle 42 the cutting knife 26 is moved upwards and afterlifting up the upper mould part 25b the vulcanized shaped piece 28 istaken out of the press tool.

In order that the shaped piece 28 may be heated and cooled down in theclosed press mould apart of the press, for example in a low-temperaturecabin or in a coolant bath, and in order that the closed mould and theshaped piece therein contained may be transported for achieving thisprocedure, the press is fitted out with Ill the automatic locking devicedescribed above, which comes automatically into action in the moment ofclicking and locks the press tool. The mode of operation of the lockingdevice is as follows:

(FIG. 4a and 4d). During the downward motion of the cutting knife 26 theinner surface of the sleeve 35 slides forth in the outer side wall ofthe bush 32 then at the end of the stroke length presses in the balls 34into the groove 33 of the carrier pin in this way in the moment ofclicking the locking of the press mould is also achieved.

FIGS. 5a-5b represent a press tool by the aid of which the periodicityof the working operation may be eliminated, that is to say, bothprevulcanization and aftervulcanization are achieved in one single pressmould and not in two templates. This is very advantageous because thenumerous working operations of the process carried out in two templates:change of the press tool, the placing in and taking out of the material,encumber and extend the production, provide opportunity for looseningworkshop discipline and falling off in quality and productivity.

The press tool represented in FIG. 5(l-Sb. consists of a die 35 and acover 36. The channel 38 formed in the body of the die 35 opens into thelower part of the shaping space 37a of the die 37 and through which aliquid employed for pressing and heat transmitting medium' for examplewater, may be conducted. Another channel 39 formed in the cover 36 opensinto the upper part of the moulding space 37. This channel 39 serves forevacuating the air driven out by the flowing-in liquid from the mouldingspace 37. The channels 38, 39 are fitted out with a closing device inorder that the liquid may flow out of the press tool at termination ofthe first stage of vulcanization. The required pressure of the liquid isprovided by a pump not represented in the figure.

The vulcanization by the aid of the press tool described above iscarried out as follows:

The crude product of small volume 41 is placed into the moulding space37 and the die 35 is closed by the cover 36. The press tool is placed onthe heating plate of the press and is pressed together at requiredpressure by the aid of the press. Liquid (water) is conducted throughthe channel 38 into the moulding space 37 and after filling up themoulding space by liquid the air evacuating channel 39 is closed down,thereupon the pressure and temperature of the tool is increased to anextent required by the first stage of vulcanization.

At the end of the first stage of vulcanization the liquid is dischargedfrom the moulding space 37 of the press mould whereupon the crude stockexpands and its in every direction growing volume fills completely themoulding space 37 of the press tool which space accurately correspondsto the form of the required prod uct (see position in conformity withFIG. 5a.)

Then the second stage of vulcanization is carried out. The temperaturerequired for this is provided by the known heatable press plate notrepresented in the figure on which the press tool is placed.

On completion of the second stage of vulcanization the press mould iscooled down and the end product is taken out of it.

As mentioned above the whole vulcanization operation has been carriedout in the very same press tool and no need for additional manipulationhas appeared. The hydraulic vulcanization course of processingillustrated in FIGS. 5a5b may be developed also in the press toolillustrated in FIGS. 3a3d which may be directly heated.

FIG. 6 represents a press tool suitable for achieving both vulcanizationstages in one and the same mould by modifying the inner space of themould, and in a mechanical way and not by hydraulic means as in theformer case.

This press tool consists of a bottom plate 42, a covering plate 43, soleinsets 44, 45, 46, 47 and of a heel inset. The sole insets may be placedinto the interior respectively taken out of it through the opening beingin the side wall of the bottom plate and the heel inset through theopening 50 being on the upper side of the cover. The cubic capacity ofthe inner moulding space may be altered by the members 44-48.

The working process using the press tool in conformity with presentinvention comprising a mould the cubic capacity of which may be alteredmechanically, is as follows:

Before putting in the crude mixture the cover 43 of the press tool isremoved, the insets 44, 45 conform to the first vulcanization stage andfitting to each other and jointly constituting the moulding space, areplaced on the bottom plate 42 and the heel inset 48 is placed on thecover 43. Thereafter the crude mixture is put into the press tool, thecover is placed on the bottom plate and fastened to it by the aid of thescrews 49, then the press tool is placed in the press where it ispressed together at required pressure meanwhile through the heatingplates the crude mixture is heated to. respectively, kept at atemperature required by the first stage of vulcanization.

On completion of the first stage of the vulcanization the cover 43 ofthe press tool is removed, the raising of the cover may be expedientlycarried out by aid of springs not illustrated in the figure the soleinsets 44, 45 are taken out and replaced by the sole insets 46, 47 whichprovide a greater cubic capacity to the moulding space. The longitudinalribs 50 of the heel insets 48 which is kept there up to the replacementof sole insets, impedes the falling out of the prevulcanized material.Thereafter the heel inset is replaced by a smaller one not illustratedin the figure which provides a greater cubic capacity. In the figurearrows A, B, C show the direction of the insertion of the insets.

On completion of these manipulations the form and the cubic capacity ofthe press tools conforms exactly to the form and dimensions of the endproduct. Thereafter the press tool is again closed and placed into theheatable press, where then the second stage of the vulcanization isachieved.

Both the heating and the cooling down are carried out by circulatingsteam respectively cold water in the channel system formed in the bottomplate respectively in the cover. By the aid of this system the intensityof heating and cooling may be increased and a fast heating up achievedat the start of the second vulcanization stage, which is of primaryimportance for the develop ment of the structure and the fast filling inof the moulding space.

The press tool is suitable for producing shaped pieces of variousdimensions in various forms and embossed at will by the use of properlyshaped replaceable insets, in one and the same press tool, larger orsmaller, right and/or left foot soles with or without embosssing may bemanufactured thus the press form of alterable cubic capacity may beexploited to the highest degree.

On constructing the press mould the expansion arising between the twovulcanization stages has been taken into account and the replaceableinsets determine the extent of the expansion as well as the finaldimensions of the finished shaped piece.

What we claim is:

1. In a process for producing closed cell, cellular, gasexpandedmaterial which comprises compounding a vulcanizable stock containing anelastomer,

a member selected from the group consisting of a plastomer, the meltingtemperature of which is equal to or less than the temperature of thefirst vulcanization step, and a thermoplastic elastomer,

a blowing agent the decomposition temperature of which is equal to orless than the temperature of the first vulcanization step, and

an accelerator system, vulcanizing said stock in two sequential stagesin a closed mold at elevated temperature. while expanding theprevulcanized stock after the first stage, cooling the vulcanizedmaterial in said closed mold, and thereafter removing the cooledvulcanized material from the mold; the improvement comprising using anaccelerator system which includes fast cross-linking in the firstvulcanization step and together with the vulcanization temperature andvulcanization time effects vulcanization in the 20-70% cross-linkingrange; carrying out both the first and the second vulcanization stagesin a completely filled mold under an external pressure of about 40-60kg/cmhu 2 in said first stage and about 20 kg/cm in said second stage,and cooling the completely vulcanized product under the latter saidpressure in said closed mold thereby hardening the plastomer componentand stabilizing the final product in a form which corresponds to theform of the closed mold used in the final vulcanization step, thusproducing a dimensionally stable microcellular material.

2. A process as claimed in claim 1, in which said first vulcanizationstep is conducted in said closed mold and said material occupies lessthan all of the volume of said closed mold in said first stage, andapplying said pressure in said first stage by introducing a liquid intosaid closed mold to surround said material, and thereafter dischargingsaid liquid from said closed mold after ensured.

1. IN A PROCESS FOR PRODUCING CLOSED CELL, CELLULAR, GASEXPANDEDMATERIAL WHICH COMPRISES COMPOUNDING A VULCANIZABLE STOCK CONTAINING ANELASTOMER, A MEMBER SELECTED FROM THE GROUP CONSISTING OF A PLASTOMER,THE MELTING TEMPERATURE OF WHICH IS EQUAL TO OR LESS THAN THETEMPERATURE OF THE FIRST VULCANIZATION STEP, AND A THERMOPLASTICELASTOMER, A BLOWING AGENT THE DECOMPOSITION TEMPERATURE OF WHICH ISEQUAL TO OR LESS THAN THE TEMPERATURE OF THE FIRST VULCANIZATION STEP,AND AN ACCELERATOR SYSTEM, VULCANIZING SAID STOCK IN TWO SEQUENTIALSTAGES IN A CLOSED MOLD AT ELEVATED TEMPERATURE, WHILE EXPANDING THEPREVULCANIZED STOCK AFTER THE FIRST STAGE, COOLING THE VULCANIZEDMATERIAL IN SAID CLOSED MOLD, AND THEREAFTER REMOVING THE COOLEDVULCANIZED MATERIAL FROM THE MOLD; THE IMPROVEMENT COMPRISING USING ANACCELERATOR SYSTEM WHICH INCLUDES A FAST CROSS-LINKING IN THE FIRSTVULCANIZATION STEP AND TOGETHER WITH THE VULCANIZATION TEMPERATURE ANDVULCANIZATION TIME EFFECTS VULCANIZATION IN THE 20-70% CROSS-LINKINGRANGE; CARRYING OUT BOTH THE FIRST AND THE SECOND VULCANIZATION STAGESIN A COMPLETELY FILLED MOLD UNDER AN EXTERNAL PRESSURE OF ABOUT 40-60KG/CMHU 2 IN SAID FIRST STAGE AND ABOUT 20 KG/CM2 IN SAID SECOND STAGE,AND COOLING THE COMPLETELY VULCANIZED PRODUCT UNDER THE LATTER SAIDPRESSURE IN SAID CLOSED MOLD THEREBY HARDENING THE PLASTOMER COMPONENTAND STABILIZING THE FINAL PRODUCT IN A FORM WHICH CORRESPONDS TO THEFORM OF THE CLOSED MOLD USED IN THE FINAL VULCANIZATION STEP, THUSPRODUCING A DIMENSIONALLY STABLE MICROCELLULAR MATERIAL.
 2. A process asclaimed in claim 1, in which said first vulcanization step is conductedin said closed mold and said material occupies less than all of thevolume of said closed mold in said first stage, and applying saidpressure in said first stage by introducing a liquid into said closedmold to surround said material, and thereafter discharging said liquidfrom said closed mold after said first stage whereupon said materialexpands and completely fills said closed mold for said second stage. 3.A process as claimed in claim 2, wherein said liquid is heated wherebyboth said pressure and said temperature required for vulcanization aresimultaneously ensured.